The invention relates to the sealing of a vitreous material onto a material containing aluminum.
One particularly worthwhile application of such seals resides in the production of electrical functional boxes which contain at least one hybrid electronic circuit, commonly referred to as "hybrid boxes." However, the invention is not confined to this particular application.
Beside monolithic integrated circuits, hybrid electronic circuits are used, being more briefly known as "hybrid circuits." Their name originates from the fact that they comprise monolithic integrated circuit chips on a ceramic substrate, the chips being associated with discrete components and links produced by metallic deposition on the ceramic material.
For certain applications, the hybrid circuits used in subunits are combined in one hybrid box. Such a box generally has a bottom, a lid and a plurality of electrical feed-through connectors situated on at least one of these walls. In certain cases, there must be hermetic seals both with regard to the connection between the bottom and the lid and with regard to the electrical feed-through connectors.
Currently known are such boxes which consist of an iron-nickel-cobalt alloy-based material which is known particularly by the trademark KOVAR of Westinghouse Corporation. Each electrical feed-through connector comprises a conductive pin generally of KOVAR hermetically fixed in a passage in the wall by a glass-to-metal seal which is well-known to a man skilled in the art. The connection between the lid and the bottom is achieved by a conventional electrical weld.
A "macrohybrid" box is a large hybrid box and producing it in KOVAR material by the aforesaid technique has two major drawbacks when such boxes are used inside computers which are mounted in an aircraft.
The first of these drawbacks is linked to the density of the KOVAR which means that the macrohybrid box has a high mass which becomes a serious disadvantage in the aforementioned use, the weight factor being particularly important in aeronautics.
The second drawback is connected to the poor heat conductivity of KOVAR. By virtue of its size, a macrohybrid box generally contains a very large number of hybrid circuits (or one very large hybrid circuit) which, in operation, give off calorific energy which is normally dissipated through the body of the box. This poor thermal conductivity of KOVAR interferes with satisfactory thermal dissipation and may, therefore, give rise to poor quality functioning, or even result in breakdowns.
It has been found that the use of an aluminum-containing material makes it possible to offset the two aforementioned disadvantages.
However, such use gives rise to considerable technical problems with regard to the production of a glass-to-aluminum seal, particularly by reason of the opposing physical properties (particularly the melting point and the coefficient of expansion) of these two materials. A man skilled in the art knows indeed that the melting point of a conventional glass is generally higher than 1000.degree. C., while the melting point of aluminum is about 550.degree. C. Furthermore, the coefficient of expansion of aluminum is generally higher than that of conventional glasses. The extent of these problems is further enhanced by the need to obtain a hermetic seal such as that normally required for macrohybrid boxes.
Therefore, the main object of the present invention is to provide a solution to this problem.